F34 4859 1901 CONTRIBUTORS TO VOL. I. JOHN G. CURTIS, M. D., Professor of Physiology in Columbia University (College of Physicians and Surgeons). W. H. HOWELL, PH. D., M. D., Professor of Physiology in the Johns Hopkins University. GRAHAM LUSK, PH. D., F. R. S. (EDIN.), Professor of Physiology in the University and Bellevue Hospital Medical College, New W. T. PORTER, M. D., Associate Professor of Physiology in the Harvard Medical School, EDWARD T. REICHERT, M. D., Professor of Physiology in the University of Pennsylvania. 47644 3 PREFACE TO THE SECOND EDITION. ADVANTAGE has been taken of the necessity of issuing a second edition of the American Text-Book of Physiology to alter somewhat its general arrangement. The book has proved to be successful, and for the most part has met only with kindly and encouraging criticisms from those who have made use of it. Many teachers, however, have suggested that the size of the book, when issued in a single volume, has constituted to some extent an inconvenience when regarded from the standpoint of a student's text-book that may be needed daily for consultation in the lecture-room or the laboratory. It has been thought best, therefore, to issue the present edition in two volumes, with the hope that the book may thereby be made more serviceable to those for whose aid it was especially written. This change in the appearance of the book has necessitated also some alteration in the arrangement of the sections, the part upon the Physiology of Nerve and Muscle being transferred to the second volume, so as to bring it into its natural relations with the Physiology of the Central Nervous System. The actual amount of material in the book remains substantially the same as in the first edition, although, naturally, very many changes have been made. Even in the short time that has elapsed since the appearance of the first edition there has been much progress in physiology, as the result of the constant activity of experimenters in this and the related sciences in all parts of the world, and an effort has been made by the various contributors to keep pace with this progress. Statements and theories that have been shown to be wrong or improbable have been eliminated, and the new facts discovered and the newer points of view have been incorporated so far as possible. Such changes are found scattered throughout the book. The only distinctly new matter that can be referred to specifically is found in the section upon the Central Nervous System, and in a short section upon the modern ideas and nomenclature of physical chemistry, with reference especially to the processes of osmosis and diffusion. The section dealing with the Central Nervous System has been recast in large part, with the intention of making it more suitable to the actual needs of medical students; while a brief presentation of some of the elementary conceptions of physical chemistry seems to be necessary at the present time, owing to the large part that these views are taking in current discussions in physiological and medical literature. The index has been revised thoroughly and considerably amplified, a table of contents has been added to each volume, and numerous new figures have been introduced. AUGUST, 1900. 5 PREFACE. THE collaboration of several teachers in the preparation of an elementary text-book of physiology is unusual, the almost invariable rule heretofore. having been for a single author to write the entire book. It does not seem desirable to attempt a discussion of the relative merits and demerits of the two plans, since the method of collaboration is untried in the teaching of physiology, and there is therefore no basis for a satisfactory comparison. It is a fact, however, that many teachers of physiology in this country have not been altogether satisfied with the text-books at their disposal. Some of the more successful older books have not kept pace with the rapid changes in modern physiology, while few, if any, of the newer books have been uniformly satisfactory in their treatment of all parts of this many-sided science. Indeed, the literature of experimental physiology is so great that it would seem to be almost impossible for any one teacher to keep thoroughly informed on all topics. This fact undoubtedly accounts for some of the defects of our present text-books, and it is hoped that one of the advantages derived from the collaboration method is that, owing to the less voluminous literature to be consulted, each author has been enabled to base his elementary account upon a comprehensive knowledge of the part of the subject assigned to him. Those who are acquainted with the difficulty of making a satisfactory elementary presentation of the complex and oftentimes unsettled questions of physiology must agree that authoritative statements and generalizations, such as are frequently necessary in text-books if they are to leave any impression at all upon the student, are usually trustworthy in proportion to the fulness of information possessed by the writer. Perhaps the most important advantage which may be expected to follow the use of the collaboration method is that the student gains thereby the point of view of a number of teachers. In a measure he reaps the same benefit as would be obtained by following courses of instruction under different teachers. The different standpoints assumed, and the differences in emphasis laid upon the various lines of procedure, chemical, physical, and anatomical, shouldgive the student a better insight into the methods of the science as it exists 6 to-day. A similar advantage may be expected to follow the inevitable overlapping of the topics assigned to the various contributors, since this has led in many cases to a treatment of the same subject by several writers, who have approached the matter under discussion from slightly varying standpoints, and in a few instances have arrived at slightly different conclusions. In this last respect the book reflects more faithfully perhaps than if written by a single author the legitimate differences of opinion which are held by physiologists at present with regard to certain questions, and in so far it fulfils more perfectly its object of presenting in an unprejudiced way the existing state of our knowledge. It is hoped, therefore, that the diversity in method of treatment, which at first sight might seem to be disadvantageous, will prove to be the most attractive feature of the book. In the preparation of the book it has been assumed that the student has previously obtained some knowledge of gross and microscopic anatomy, or is taking courses in these subjects concurrently with his physiology. For this reason no systematic attempt has been made to present details of histology or anatomy, but each author has been left free to avail himself of material of this kind according as he felt the necessity for it in developing the physiological side. In response to a general desire on the part of the contributors, references to literature have been given in the book. Some of the authors have used these freely, even to the point of giving a fairly complete bibliography of the subject, while others have preferred to employ them only occasionally, where the facts cited are recent or are noteworthy because of their importance or historical interest. References of this character are not usually found in elementary text books, so that a brief word of explanation seems desirable. It has not been supposed that the student will necessarily look up the references or commit to memory the names of the authorities quoted, although it is possible, of course, that individual students may be led to refer occasionally to original sources, and thereby acquire a truer knowledge of the subject. The main result hoped for, however, is a healthful pedagogical influence. It is too often the case that the student of medicine, or indeed the graduate in medicine, regards his text-book as a final authority, losing sight of the fact that such books are mainly compilations from the works of various investigators, and that in all matters in dispute in physiology the final decision must be made, so far as possible, upon the evidence furnished by experimental work. To enforce this latter idea and to indicate the character and source of the great literature from which the material of the text-book is obtained have been the main reasons for the adoption of the reference system. It is hoped also that the |